Device for compensating elastic after-effects or creeping

ABSTRACT

The present device prevents the transmission of creeping from a structural element to another structural element such as a measuring device, by means of an intermediate member positioned between the measuring device and the structural element. The material of the intermediate member is selected so that its creeping characteristics compensate the creeping of the structural element. The intermediate member may be further selected to also compensate for creeping due to temperature changes.

United States Patent [191 [111 3,735,32 Birkholtz May 22, 1973 [54]DEVICE FOR COMPENSATING [56] References Cited ELASTIC AFTER-EFFECTS ORUNITED STATES PATENTS CREEPING 3,451,030 6/1969 Garfinkel ..338/2 [75]Inventor: Gottfried Birkholtz, weiterstadt, 3,137,834 6/1964 Pfann73/885 R X Germany 2,933,665 4/1960 Dimeff ..317/246 [73] Assignee:Firma Carl Schenck Maschinenf b ik GmbH, Darmstadt, Germany PrzmaryExammerC. L. Albntton An -W. G. F 22 Filed: Sept. 13, 1971 asse [21]Appl. No.2 179,976 [57] ABSTRACT The present device prevents thetransmission of creep- [30] Foreign Application Priority Data ing from astructural element to another structural element such as a measuringdevice, by means of an in- Sept. 23, 1970 Germany ..P 20 46 855.7termediate member positioned between the measuring [52] U 8 Cl 338/2338/3 device and the structural element. The material of the [51] In} .0G0; I 1/22 intermediate member is Selected so that its p g [58] FieldoisiiiIIIIIIIIfIIIIIIIIIIESm 3 5 6- characteflsics mpensate creeping the317/246; 73/88.5 R, 88.5 SD

tural element. The intermediate member may be further selected to alsocompensate for creeping due to temperature changes.

5 Claims, 3 Drawing Figures DEVICE FOR COMPENSATING ELASTICAFTER-EFFECTS OR CREEPING BACKGROUND OF THE INVENTION The presentinvention relates to a device for compensating the effects of creeping.More specifically, the present device prevents the transfer of creepingeffects from elastically deformable structural elements to otherstructural elements such as measuring devices attached to the firstmentioned structural elements. Such creeping effects may be the resultof forces and/or temperature changes to which said first mentionedstructural elements may be subjected. An elastically deformablestructural element may be, for example, the measuring spring in ameasuring means such as a gauge.

The theory of elasticity defines the term creeping as a time responsivedeformation of a body after a force has acted on the body. The meaningor connotation of creeping" may also be expressed as an elastic aftereffect. Creeping is reversible and it is dependent on the temperature,the load, and the time period during which the load acts on the body.For example, the creeping effect in a measuring gauge such as atensiometer, a pressure gauge, or the like causes a change of thereading as a function of time. In other words, the reading does notremain the same as a function of time when a given, constant force ifeffective on an elastically deformable body. Those skilled. in the artwill appreciate that such an effect constitutes a serious disadvantagebecause it impairs the accurate ascertaining of forces which areactually effective on a structural element.

OBJECTS OF THE INVENTION In view of the foregoing it is an object of thepresent invention to provide a device which will prevent the creepingeffect from affecting the measuring of elcstic deformations of elasticstructural elements.

Another object of the invention is to compensate the creeping effect ofa structural element by selecting the creeping characteristics of anintermediate member so that said effect will not be transmitted toanother structural element.

Yet another object of the invention is to interpose a creeping effectcompensating member between two structural elements whereby thecompensating member has a creeping characteristic which is substantiallymore pronounced than the creeping characteristic of each of saidelements.

A still further object of the invention is to provide an intermediatemember which absorbs the creeping from an adjacent structural element sothat the creeping is not transferred to another adjacent structuralelement.

SUMMARY OF THE INVENTION According to the invention there is provided acreeping effect compensating device in which an intermediatecompensating member is operatively located between an elasticallydeformable structural element and another structural element such as thesupport for a measuring means. The compensating intermediate member hasa creeping characteristic of its own which is such that the creeping ofthe intermediate member prevents the transmission of the creeping of onestructural element to the other.

The creeping of the intermediate member which is caused by the creepingof the elastically deformable structural element and by the load exertedon the intermediate member by the other structural element, such as asupporting element for a measuring means, prevents the transfer of thecreeping of the structural element to said measuring means.

BRIEF FIGURE DESCRIPTION In order that the invention may be clearlyunderstood, it will now be described, by way of example, with referenceto the accompanying drawings, wherein:

FIG. 1 is a cross-section through one embodiment of a creepingcompensating device according to the invention shown in its restposition, that is, wherein no force has as yet been applied to theelastically deformable element;

FIG. 2 shows the section of FIG. 1 immediately after a load has beenapplied to the device; and

FIG. 3 illustrates the section of FIG. 1 after the load has beeneffective on the device for a certain period of time.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT The present device maybest be understood by considering the state of the device at threedifferent times as illustrated by the three figures.

An elastically deformable structural element 1, which is to be subjectedto a load or force, may, for example, be the measuring spring of ameasuring means such as a tensiometer or pressure gauge. A creepingcompensating intermediate member 3 is applied to the structuralelement 1. Another structural element 4, such as the support for ameasuring means 5 for measuring, for example, the elongation of thestructural element l is applied to the opposite surface of theintermediate member 3. A bonding agent 2 connects the structural element1 to the intermediate member 3 as well as to the supporting element 4.The bonding agent may be selected from a large group of bonding agents,but may not possess the properties or characteristics of a viscousliquid. High strength bonding agents, for instance tempered, hardenablemulti-component resins such as epoxy resins, have been found to beadvantageous for the present purpose of bonding the surfaces of theintermediate member to the adjacent structural elements.

FIG. 1 shows the device in the rest position, that is prior to theapplication of any force or load. In FIG. 2 the structural element 1 hasbeen subjected to acting and reacting forces indicated by the arrows 6and 6a. Under the influence of these forces 6,60 the elastic structuralelement 1 expands by a length corresponding to (2 X a) whereby itstretches the bottom side or surface 3a of the intermediate member 3 bya length corresponding to (2 X b). This length (2 X b) depends on theelongation a of the structural element 1 and on the relative dimensionsof the elements 1 and 3. Preferably, the intermediate member 3 shouldhave approximately the same length as the structural element 1 so thatthe elongation a" of the element 1 is approximately equal to theelongation b of the intermediate member 3. The elongation (2 X b) of thebottom surface 3a of the intermediate member 3 stretches the top surface3b thereof by a length (2 X c). This elongation or stretching (2 X c) istransmitted to the supporting element 4 of the measuring means or gauge5. Consequently, the supporting element 4 and the measuring means areelongated by a length corresponding to (2 X c).

The supporting element 4 is made of a very hard material, which eitherdoes not creep at all under load, or only to a very minor degree.Therefore, the elongation (2 X c) of the supporting element 4 and of themeasuring means 5 is somewhat smaller than the elongation (2 X a) of thestructural element 1. However, this does not amount to any disadvantagesince the elongation (2 x c) of the measuring means 5 is strictlyproportional to the elongation (2 X a) of the structural element 1.

Besides, the just mentioned reduction may be easily compensated byappropriate means, for instance by providing appropriate electricalamplification in connection with a measuring means such as a pressure orstrain gauge as is well known in the art. However, such amplification isnot necessary in most instances, since the loss is very small. It hasbeen ascertained in experiments that the loss is of the .order of about1 percent.

Over a period of time the elastic structural element 1 is furtherelongated due to creeping by a length corresponding to (2 X d) as shownin FIG. 3. As a result, the bottom surface or side 30 of theintermediate member 3 is also elongated by a length corresponding to (2X e). This length (2 X e) depends on the ratio of the lengths of theelements 1 and 3.

The material of which the intermediate element 3 is made as taughtherein, is selected so that its creeping characteristics are morepronounced than those of the structural element 1. Therefore, the bottomside 3a of the intermediate member 3 creeps in unison with thestructural element 1 whereas the top side 3b of the intermediate member3 is not deformed at all. This gist of the invention provides thedesired compensation. Since the top surface 3b of the intermediateelement 3 is connected to the supporting element 4 of the measuringmeans 5 and since said supporting element 4 does not creep to anymeasurable extent, the creeping of the element 1 is not transmitted tothe measuring means 5. Accordingly, the creeping of the structuralelement 1 does not cause any deformation of the supporting element 4 norof the measuring means 5.

In view of the foregoing it will be appreciated that the creeping of theelastic structural element 1 is compensated in such a manner that theelongation of the tensiometer remains constant as a function of time sothat it depends solely on the load and is independent of the creeping.

According to the invention it is further possible to compensate thetemperature creeping characteristics of the structural element 1 by anappropriate selection of the material for making the intermediate member3. Stated differently the temperature creeping characteristics of theintermediate member 3 compensate the respective characteristics of thestructural element 1. In this embodiment the elogation of the measuringmeans 5 is also independent of the temperature.

What is claimed is:

l. A strain gauge device comprising a strain gauge, an elasticallydeformable structural element having a given creeping characteristic, asupport for said strain gauge also having a given creepingcharacteristic, at least one intermediate member arranged between saidsupport and said elastically deformable structural element, means forbonding said intermediate member to said support and to said elasticallydeformable structural element, said intermediate member having acreeping characteristic which is substantially more pronounced than saidgiven creeping characteristics whereby the effects of creeping of saidstructural element on said strain gauge are avoided by preventing thetransmittal of said creeping effects from said structural element tosaid strain gauge through said intermediate member.

2. The device according to claim 1, wherein said intermediate member isa material having a creeping temperature characteristic capable ofcompensating for the creeping-temperature characteristic of saidelastically deformable structural element.

3. The device according to claim 1, wherein said bonding means betweenthe support and the intermediate member as well as the bonding meansbetween the intermediate member and the structural element comprisebonding resin.

4. The device according to claim 1, wherein said bonding resin comprisesa multi-component bonding resin which is a tempered, high strength,curable resin.

5. The device according to claim 1, wherein said support is made of ahard material having a creeping effect which is small or zero.

1. A strain gauge device comprising a strain gauge, an elasticallydeformable structural element having a given creeping characteristic, asupport for said strain gauge also having a given creepingcharacteristic, at least one intermediate member arranged between saidsupport and said elastically deformable structural element, means forbonding said intermediate member to said support and to said elasticallydeformable structural element, said intermediate member having acreeping characteristic which is substantially more pronounced than saidgiven creeping characteristics whereby the effects of creeping of saidstructural element on said strain gauge are avoided by preventing thetransmittal of said creeping effects from said structural element tosaid strain gauge through said intermediate member.
 2. The deviceaccording to claim 1, wherein said intermediate member is a materialhaving a creeping temperature characteristic capable of compensating forthe creeping-temperature characteristic of said elastically deformablestructural element.
 3. The device according to claim 1, wherein saidbonding means between the support and the intermediate member as well asthe bonding means between the intermediate member and the structuralelement comprise bonding resin.
 4. The device according to claim 1,wherein said bonding resin comprises a multi-component bonding resinwhich is a tempered, high strength, curable resin.
 5. The deviceaccording to claim 1, wherein said support is made of a hard materialhaving a creeping effect which is small or zero.